The goal of the project is to synthesize bifunctional ligands which have a high affinity for Pb(II) and Bi(III) by virtue of the presence of sulfur donor atoms. simple thiolate ligands such as dimercaptosuccinic acid have been shown to form complexes of high stability with both ions (Kf for the 1:2 BiDMSA complex in log 43.87), yet appropriate multidentate chelating agents suitable for linkage to monoclonal antibodies are not yet available. As such, systematic exploration of the chemistry of incorporating thiol donor groups into both existing and new acyclic and cyclic chelating agents is planned. Appropriated precursor molecules will be synthesized to allow testing of the methodology for the incorporation of thiols into new chelating agents for protein modification.